From 2c360c2131f0838c0653fa08d0e6dc448d8564c2 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Johannes=20L=C3=B6thberg?= <johannes@kyriasis.com>
Date: Fri, 9 Sep 2022 20:26:52 +0200
Subject: [PATCH] Set `TCP_NODELAY` on the `TcpStream` to disable Nagle's
 algorithm.
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Due to the way the `async-h1` crate writes HTTP responses to the `TcpStream` the head
and body end up in separate write calls to the underlying socket.  If we're responding
to more than one request received from the same `TcpStream` it means that we did two
sends and then tried to read.  That read can take up to 500 milliseconds to complete due
to bad interactions between Nagle's algorithm and delayed ACK.  (In practice this is 40
ms on Linux.)

Disabling Nagle's algorithm works around this until `async-h1` is fixed.

https://github.com/http-rs/async-h1/issues/199

Signed-off-by: Johannes Löthberg <johannes@kyriasis.com>
---
 src/listener/tcp_listener.rs | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/src/listener/tcp_listener.rs b/src/listener/tcp_listener.rs
index 03be652e..25902aec 100644
--- a/src/listener/tcp_listener.rs
+++ b/src/listener/tcp_listener.rs
@@ -47,6 +47,22 @@ impl<State> TcpListener<State> {
 
 fn handle_tcp<State: Clone + Send + Sync + 'static>(app: Server<State>, stream: TcpStream) {
     task::spawn(async move {
+        // Set `TCP_NODELAY` on the `TcpStream` to disable Nagle's algorithm.
+        //
+        // Due to the way the `async-h1` crate writes HTTP responses to the `TcpStream` the head
+        // and body end up in separate write calls to the underlying socket.  If we're responding
+        // to more than one request received from the same `TcpStream` it means that we did two
+        // sends and then tried to read.  That read can take up to 500 milliseconds to complete due
+        // to bad interactions between Nagle's algorithm and delayed ACK.  (In practice this is 40
+        // ms on Linux.)
+        //
+        // Disabling Nagle's algorithm works around this until `async-h1` is fixed.
+        //
+        // https://github.com/http-rs/async-h1/issues/199
+        if let Err(err) = stream.set_nodelay(true) {
+            error!("Failed to set TCP_NODELAY: {}", err);
+        }
+
         let local_addr = stream.local_addr().ok();
         let peer_addr = stream.peer_addr().ok();